The invention relates to a method for measuring the direction and force of gaseous or liquid flows, herein referred to as fluid flows or fluid currents for short, as well as to a probe which can be used in this method.
Many measuring instruments for measuring fluid flows and particularly wind measuring instruments are already known. The field of application for flow measuring instruments includes all fields in which flows are of importance, for example meteorology, aircraft, ships, motor vehicles, wind tunnel measurements and so forth. Even if the measuring problems differ from each other in detail, the fundamental requirement of the flow measuring instrument is, nevertheless, that this measuring instrument should disturb the flow to be measured as little as possible. In addition, the existence of moving parts in a measuring device is undesirable since the moving parts usually produce particularly strong disturbances of the flow and are generally not free from inertia and hysteresis effects. For this reason, problems previously occurred in this respect especially if the direction of a flow had to be measured. If, on the other hand, inertia or hysteresis effects of rotating parts on flow measuring instruments had to be reduced, the bearings of the rotating parts had to be improved which, in turn, led either to an increase in the weight of the measuring probe or made the measuring probe mechanically sensitive to jarring, shocks, vibrations and so forth. However, in rough operation on ships or in aircraft, neither heavy probes nor probes which are mechanically too sensitive can be used.
In the case of the measuring of a flow with aircrafts, helicopters or other flying objects, the direction of the airflow onto and around the flying object has to be measured, as well as the force of the flow and the velocity. For measurements of this kind, measuring probes are still used which rest on the Prandtl principle of the known pressure probes for measuring the static pressure, on the Pitot-tube, which is used to measure the sum of the dynamic pressure and the static pressure, and on the pressure tube. This latter pressure tube is essentially a Pitot-tube in combination with a necessary pressure probe for measuring the static pressure and permitting the determination of the dynamic pressure. Knowledge of the dynamic pressure is desirable, since from it the velocity of aircrafts, as well as their course may be determined.
The traditional measuring instruments, which rest on these principles, display various disadvantages. One of these is that the measuring range of the angle is relatively small on pressure tubes. With pressure tubes one may only achieve good measuring accuracy with impact angles up to 10 degrees. When, however, an aircraft, for example, takes off during strong air currents, when an accurate knowledge of the current conditions is especially important, the traditional pressure tubes often fail because they are blown upon from too slanted an angle. Furthermore, the determination of the static pressure is difficult because the air movements can falsify a predetermined altitude compensation, not taking into consideration, that such altitude compensation is expendable. Of course, it is therefore desirable to use a measuring probe with which such difficulties do not arise. In addition, to the great need for an improved probe in aeronautical applications, similar problems also exist with respect to navigational problems as well as problems in other fields in which fluid flows play a role and in which the flows must be measured such as in meteorology.
The present invention, therefore, has the object of creating a method for measuring gaseous or liquid flows, as well as a probe for use in this method, which can be used for measuring particularly the direction of the flow and also the force of the flow and which is lightweight, has no moving parts and can be constructed in a stream-lined manner so that it causes little disturbance of the actual flow to be measured.
Another object of the present invention is to provide a method, and a probe for use in the method, which utilizes a wide impact angle measuring range with which either dynamic pressures may be measured directly, without additionally having to determine the static pressure, or with which only static pressure is measured, if only static pressure is desired.
Still another object of the present invention is to provide a probe which is simple in construction yet functionally reliable and variously adaptable.